Abstract

Magnetic instability in both ultrapure and carbon-doped films is investigated by magneto-optical imaging, transport, and bulk magnetization measurements. In the carbon-doped thin films, familiar dendritic flux-jump patterns were observed at low temperature as reported in previous experiments. In the ultrapure thin film, however, a remarkably stable flux penetration was observed, clearly showing the classic behavior of the critical state model. Such different behavior indicates that the electron scattering ultimately controls the magnetic stability of the films.

Received 21 June 2004Accepted 30 September 2004Published online 01 December 2004

Acknowledgments:

The authors would like to thank Dr. L. Cooley for critical reading of this manuscript. The work at BNL was supported by the U.S. Department of Energy, Office of Basic Energy Science, under Contract No. DE-AC-02-98CH10886. The work at Penn State is supported in part by ONR under Grant Nos. N00014-00-1-0294 (X.X.X.) and N0014-01-1-0006 (Redwing), by NSF under Grant Nos. DMR-0306746 (X.X.X. and J.M.R.), DMR-0405502 (Q.L.).